The field of imaging can be divided into one-dimensional (1D) or linear imaging, two-dimensional (2D) imaging, and three-dimensional imaging.
Examples of 1D imagers include bar code devices using linear pixelated detectors, including for instance charge-coupled-device (CCD) and complementary-metal-oxide-silicon (CMOS) detectors. Linear pixelated imagers typically include illumination to reduce exposure time and ambient lighting requirements, often in the form of a sheet of light formed by a light emitting diode (LED) or LED array. Line-Scan cameras are a specific type of 1D pixelated imager. In line-scan cameras, a second dimension, usually perpendicular to the detector array, is provided by movement of the object or phenomenon being photographed.
2D imagers are used for myriad applications, including for instance, automated inspection, automated vehicle guidance, 2D symbol reading, omni-directional linear symbol reading, document capture, signature capture, endoscopic and laparoscopic visualization, and many other important applications. The most familiar form of 2D imaging is perhaps the digital camera, available in both still and video variants. Generally, 2D imagers use 2D pixelated arrays such as 2D CCD and 2D CMOS detectors. Often, 2D imagers include illuminators to improve low-light performance, depth-of-field, and motion blur immunity. 2D imagers are characterized by field-of-view (FOV) having both height and width.
Both linear and 2D imagers commonly trade off several performance characteristics including depth-of-field, resolution, and motion blur immunity. Frequently, designers choose to add illumination to the system. In such situations, peak power consumption and illuminator cost vs. DOF may be regarded as design trade-offs.
In typical pixelated imagers, each pixel in an array receives light energy from a conjugate point in the field-of-view for a selected sampling interval. Each pixel converts light to electrical charge that accumulates proportionally to the brightness of its conjugate point.
Another familiar field of imaging is that of film photography. Film photography is widely practiced and widely understood in terms of the trade-offs between depth-of-field (determined by lens f-stop), motion blur immunity (determined by shutter speed), resolution, and dynamic range (both of the latter determined largely by film chemistry and film speed). Flash photography adds illumination to the field-of-view to enable operation in dark or fast-moving environments. Unfortunately, flash photography suffers from dynamic range issues, having a tendency to overexpose nearby objects while underexposing distant parts of the FOV.
Another field that relates to the present invention is that of laser scanning. Laser scanning systems scan a beam, typically a laser beam, over a surface and measure the light reflected from the beam. Generally, laser scanners detect light instantaneously scattered by the moving spot without imaging it onto a detector array. Rather, the size of the projected spot itself determines resolution and the detector may be of a non-imaging type such as a PIN photo-diode or the like. Some laser scanners sequentially form a non-coincident pattern of scan lines such as a raster pattern or a “starburst” pattern. These can be especially useful for multiple symbol and stacked 2D symbol reading, or omni-directional bar code reading, respectively.
Scanned beam systems, in the form of conventional linear (1D) bar code scanners have been in use since the mid-1970 s as fixed mount devices such as those used in grocery stores. By the early 1980 s, scanned beam systems had been adapted to hand held form as several bar code companies introduced helium-neon based hand held scanners, most commonly called laser scanners. In such systems, the pattern of received light is referred to as the scan reflectance profile and may be processed to decode bar code symbols through which the beam is scanned.
Scanned beam bar code systems have not generally heretofore been referred to as “imagers”, because they generally do not capture an image per se. Instead, they continuously scan a beam and simply monitor the reflected light for a scan reflectance profile that is indicative of a bar code symbol.
In more recent times, scanning laser systems have found use in other image capture applications, such as scanning laser ophthalmoscopes and scanning microscopes.
Another related field is that of illumination systems for image capture. Used in still photography as well as cinematic and video photography, such illumination systems are used to achieve effects not possible with ambient light. Consumer systems typically include a simple strobe (for still photography) or incandescent light (for video photography) that emits more-or-less uniform light across the entire field-of-view. Often, the resulting images have too much contrast, foreground objects being over-exposed and the background underexposed. Commercial and industrial photographers and cinematographers frequently add multiple illuminators to a scene to try to recapture some of the ambiance that is lost in simple consumer systems. These attempts to manually manipulate the illumination intensity across the field of view are frequently laborious and require a high degree of artistry.